This invention relates to a fluid injector for the introduction, dispersion, and mixing of a first fluid into a second fluid flowing through a conduit. More particularly, this invention relates to a fluid injector for injecting a highly corrosive fluid, such as hydrochloric acid, into a flowing stream maintained at high temperature and pressure, such as a stream of hot geothermal brine, for the purpose of controlling scaling in the brine-handling equipment without the rapid corrosion to the injector and associated conduits usually attendant in the environment of hot acidified brine.
In the course of producing energy from hot geothermal brine streams, it is known to acidify the hot brine to reduce the production of scale in liquid-handling equipment. Because geothermal brines have been confined in reservoir rock at high temperature and pressure for long periods of time, produced brines are super-saturated with scale-forming constituents dissolved from the reservoir rocks. Upon production from the reservoir, the brine undergoes reduction in temperature and pressure sufficient to cause extensive precipitation of scales from the supersaturated liquid, so that the liquid-handling equipment becomes clogged with scale and, over time, can become completely inoperative. Since the deposition of scales is reduced by addition of acid, it is known to acidify brines to control scaling in geothermal liquid-handling equipment. But the acid used to control scaling can attack and severely corrode the injection apparatus and surrounding conduits. Corrosion to the interior of the injector can be minimized by using acid resistant alloys. However, the combination of hot acid and geothermal brine is many times more corrosive to metals than hot acid alone. Contact of acid in hot brine with the exterior of the injector and nearby conduits can result in corrosion so severe as to rapidly destroy liquid handling equipment made from even the most corrosion resistant alloys.
Apparatus used to inject a small fluid stream into a larger fluid stream and to mix the small stream with the larger may depend upon turbulence created by the body of a nozzle in the larger stream. U.S. Pat. No. 4,114,195 to Dirksing, et al. discloses an injector having an elongated body, such as a pipe, mounted through an aperture in the side of a larger conduit transversely to the flow of the larger stream therein. An axial bore through the body of the injector permits introduction and mixing into the additive stream within the injector of a small portion of fluid from the large stream before injection into the large fluid stream. The mixture enters the large stream via openings at each end of a small T-shaped extension having connection with the axial bore and is thereby disbursed into the flowing stream. Additional mixing occurs downstream of the conduit as the result of turbulence in the flowing stream caused by presence of the injector.
A hydrofoil shaped injector may also be used to control the path of the additive once it is introduced into the fluid stream. U.S. Pat. No. 4,026,527 to Costen discloses a hydrofoil-shaped vortex generator which controls dispersion of an effluent into a liquid stream, such as a river. An effluent liquid is ejected through tips extending from the extreme ends of an injector having a T shaped transverse wing-like member shaped as a hydrofoil. Vortices are created by the hydrofoil at its extreme ends in the flowing stream. The effluents from each tip are entrained in the vortical flow. By selectively positioning the vortex-generator, effluents can be carried away from the mixing point by the vortices without mixing into the stream at large. The strength and duration of the vortical flow will depend upon factors such as the lift coefficient of the hydrofoil and the speed and turbulence of the flowing streams. The hydrofoil generator is particularly useful for carrying the additive away from the point of dispersion without mixing it into the larger flowing stream. This type of hydrofoil generator, while useful for preventing backmixing and providing directional flow to the additive, does not disburse the additive in a uniform manner into the fluid stream as would be desired in an injector used to acidify brine. To prevent precipitation of scale from hot brine, the acid must be mixed thoroughly into the brine within a short distance of the point of injection.
U.S. Pat. No. 3,297,305 to Walden combines a static mixing device with an injection nozzle to promote thorough mixing of a chemical into a flowing stream. Disposed within a tubular mixing chamber, such as a conduit containing flow of a large fluid stream, is a plurality of mixing vanes spaced longitudinally within the mixing chamber. Each vane extends radially outward from a central point at an angle sufficient to impart to the larger stream a swirling movement, each mixing vane being arranged to reverse the swirling movement imparted to the flowing stream by the preceding vane. Ahead of the mixing vanes is an injector tube mounted from the side of the conduit which extends transversely as far as the axial midpoint of the mixing chamber. A laterally-extending nozzle directed axially against the intended flow of the larger fluid stream extends from the injector tube. The nozzle is conically shaped and comprises a flexible diaphragm having orifices adapted to deform or stretch in response to increased pressure in the discharge nozzle caused by clogging of dirt or chemical particles. The expandable orifices are self-cleaning, should plugging occur from within. The additive fluid is injected from the nozzle into the flowing stream, and turbulence produced by the vane mixers thoroughly disperses the additive into the larger stream. The nozzle disclosed by Walden, however, is unsuitable for use with a highly corrosive acid. The injected fluid is not disbursed radially away from the nozzle itself to prevent contact of the additive with its exterior. Moreover, since the nozzle injects the additive against the flow of the current, the chemical additive flows across the injection nozzle. If the additive were a highly corrosive acid such as hydrochloric acid used in control of scale from geothermal brine, the concentrated acid would corrode the exterior of the injection nozzle beyond use in a relatively short period of time.
The problems unique to injection of a highly corrosive scale-inhibiting additive into a high temperature geothermal stream therefore are not solved by injection nozzles known in the art. What is particularly needed is an injection nozzle which disburses the corrosive additive away from the nozzle in a uniform manner. Uniform dispersion directed away from the nozzle assures that the nozzle is not subject to rapid corrosion, and that the additive will effectively reduce scaling in the interior of the conduit without excessive corrosion to the walls of the conduit.